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          <h1 class="post-title" itemprop="name headline">js原型链污染</h1>
        

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        <h2 id="写在前面"><a href="#写在前面" class="headerlink" title="写在前面"></a>写在前面</h2><p>已经遇见过好几道原型链污染的题目了,一直没有整体学习整理过.国赛又碰见了,然而没做出来,痛定思痛,准备学习一下.<br><a id="more"></a></p>
<h2 id="原型与原型链"><a href="#原型与原型链" class="headerlink" title="原型与原型链"></a>原型与原型链</h2><p>JavaScript是一门面向对象语言，有意思的一点是，它语法中并没有class的概念，但是它仍然大量使用了对象。为了保证对象之间的联系，JavaScript引入了原型和原型链的概念。</p>
<h3 id="构造函数与原型"><a href="#构造函数与原型" class="headerlink" title="构造函数与原型"></a>构造函数与原型</h3><p>为了保证JavaScript“看起来像Java”，JavaScript中也加入了new操作符：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> obj = <span class="keyword">new</span> FunctionName()</span><br></pre></td></tr></table></figure>
<p>但与Java不同的是,JavaScript中的new操作符后面跟的并不是类名而是函数名,JavaScript并非通过类二十直接通过构造函数来创建实例。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Dog</span>(<span class="params">name, color</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name</span><br><span class="line">    <span class="keyword">this</span>.color = color</span><br><span class="line">    <span class="keyword">this</span>.bark = <span class="function"><span class="params">()</span> =&gt;</span> &#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="string">'wangwang~'</span>)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> dog1 = <span class="keyword">new</span> Dog(<span class="string">'dog1'</span>, <span class="string">'black'</span>)</span><br><span class="line"><span class="keyword">const</span> dog2 = <span class="keyword">new</span> Dog(<span class="string">'dog2'</span>, <span class="string">'white'</span>)</span><br></pre></td></tr></table></figure>
<p>上述代码就是JavaScript中通过构造函数创建实例的过程,但这种方式有一个很大的问题。通过构造函数创建实例的时候，每创建一个实例，都需要重新创建这个方法，再把它添加新的实例中。<br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/3.jpg" alt="test"><br>这样就造成了很大的浪费，所以需要一种方法来解决这个问题。<br><code>原型(prototype)</code>的使用就是为了解决这个问题：</p>
<ul>
<li><p>每一个构造函数都拥有一个prototype属性，这个属性指向一个对象，也就是原型对象。当使用这个构造函数创建实例的时候，prototype属性指向的原型对象就成为实例的原型对象。</p>
</li>
<li><p>原型对象默认拥有一个constructor属性，指向指向它的那个构造函数（也就是说构造函数和原型对象是互相指向的关系）。</p>
</li>
<li><p>每个对象都拥有一个隐藏的属性<code>prototype</code>，指向它的原型对象，这个属性可以通过 Object.getPrototypeOf(obj) 或 obj.<strong>proto</strong> 来访问。<br>例如上述代码<br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/1.jpg" alt="test"></p>
</li>
<li><p>如上文所述，原型对象就是用来存放实例中共有的那部分属性。</p>
</li>
<li><p>在JavaScript中，所有的对象都是由它的原型对象继承而来，反之，所有的对象都可以作为原型对象存在。</p>
</li>
<li><p>访问对象的属性时，JavaScript会首先在对象自身的属性内查找，若没有找到，则会跳转到该对象的原型对象中查找。</p>
</li>
</ul>
<p>上述代码中各对象关系可表示为下图<br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/2.png" alt="test"></p>
<p>通过原型,我们可以将上述代码修改为:</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Dog</span>(<span class="params">name, color</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name</span><br><span class="line">    <span class="keyword">this</span>.color = color</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">Dog.prototype.bark = <span class="function"><span class="params">()</span> =&gt;</span> &#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">'wangwang~'</span>)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/4.jpg" alt="test"><br>实例化dog1和dog2,我们发现他们bark函数相同,也就解决了之前的问题.</p>
<h3 id="原型链与继承"><a href="#原型链与继承" class="headerlink" title="原型链与继承"></a>原型链与继承</h3><p>上文提到，JavaScript中所有的对象都是由它的原型对象继承而来。而原型对象自身也是一个对象，它也有自己的原型对象，这样层层上溯，就形成了一个类似链表的结构，这就是<code>原型链（prototype chain）</code>。</p>
<p>所有原型链的终点都是Object函数的prototype属性，因为在JavaScript中的对象都默认由Object()构造。Objec.prototype指向的原型对象同样拥有原型，不过它的原型是null，而null则没有原型。</p>
<p>通过原型链就可以在JavaScript中实现继承，JavaScript中的继承相当灵活，有多种继承的实现方法，这里只介绍一种最常用的继承方法也就是组合继承。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Dog</span>(<span class="params">name, color</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name</span><br><span class="line">    <span class="keyword">this</span>.color = color</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">Dog.prototype.bark = <span class="function"><span class="params">()</span> =&gt;</span> &#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">'wangwang~'</span>)</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Husky</span>(<span class="params">name, color, weight</span>) </span>&#123;</span><br><span class="line">    Dog.call(<span class="keyword">this</span>, name, color)</span><br><span class="line">    <span class="keyword">this</span>.weight = weight</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">Husky.prototype = <span class="keyword">new</span> Dog()</span><br></pre></td></tr></table></figure>
<p>这里声明了一个新的构造函数Husky，通过call方法继承Dog中的属性（call方法的作用可以简单理解为将Dog中的属性添加到Husky中，因为还涉及到其他的知识点所以不多赘述），并添加了一个weight属性。然后用Dog函数创建了一个实例作为Husky的原型对象赋值给Husky.prototype以继承方法。这样，通过Husky函数创建的实例就拥有了Dog中的属性和方法。</p>
<h2 id="原型链污染"><a href="#原型链污染" class="headerlink" title="原型链污染"></a>原型链污染</h2><p>为了更方便描述，我们修改一下之前的代码</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Dog</span>(<span class="params">name</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">this</span>.name = name</span><br><span class="line">    <span class="keyword">this</span>.color = <span class="string">"white"</span></span><br><span class="line">    <span class="keyword">this</span>.bark = <span class="function"><span class="params">()</span> =&gt;</span> &#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="string">'wangwang~'</span>)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Husky</span>(<span class="params">name, weight</span>) </span>&#123;</span><br><span class="line">    Dog.call(<span class="keyword">this</span>, name)</span><br><span class="line">    <span class="keyword">this</span>.weight = weight</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">Husky.prototype = <span class="keyword">new</span> Dog()</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> dog1 = <span class="keyword">new</span> Husky(<span class="string">'dog1'</span>, <span class="number">50</span>)</span><br><span class="line"><span class="keyword">const</span> dog2 = <span class="keyword">new</span> Husky(<span class="string">'dog2'</span>, <span class="number">100</span>)</span><br></pre></td></tr></table></figure>
<p>我们发现如果修改dog1.<strong>Proto</strong>.color = 1, dog2的color也会改变,这样的操作污染了原型链,称之为原型链污染.<br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/5.png" alt="test"><br>也就是,在一个应用中，如果攻击者控制并修改了一个对象的原型，那么将可以影响所有和这个对象来自同一个类、父祖类的对象。这种攻击方式就是原型链污染。</p>
<h2 id="实例"><a href="#实例" class="headerlink" title="实例"></a>实例</h2><h3 id="hackit-2018"><a href="#hackit-2018" class="headerlink" title="hackit 2018"></a>hackit 2018</h3><p><a href="https://github.com/meizjm3i/CTF-Challenge/tree/master/nodejs/chall_4" target="_blank" rel="noopener">源码地址</a></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> express = <span class="built_in">require</span>(<span class="string">'express'</span>)</span><br><span class="line"><span class="keyword">var</span> hbs = <span class="built_in">require</span>(<span class="string">'hbs'</span>);</span><br><span class="line"><span class="keyword">var</span> bodyParser = <span class="built_in">require</span>(<span class="string">'body-parser'</span>);</span><br><span class="line"><span class="keyword">const</span> md5 = <span class="built_in">require</span>(<span class="string">'md5'</span>);</span><br><span class="line"><span class="keyword">var</span> morganBody = <span class="built_in">require</span>(<span class="string">'morgan-body'</span>);</span><br><span class="line"><span class="keyword">const</span> app = express();</span><br><span class="line"><span class="keyword">var</span> user = []; <span class="comment">//empty for now</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> matrix = [];</span><br><span class="line"><span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i &lt; <span class="number">3</span>; i++)&#123;</span><br><span class="line">    matrix[i] = [<span class="literal">null</span> , <span class="literal">null</span>, <span class="literal">null</span>];</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">draw</span>(<span class="params">mat</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">var</span> count = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i &lt; <span class="number">3</span>; i++)&#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">var</span> j = <span class="number">0</span>; j &lt; <span class="number">3</span>; j++)&#123;</span><br><span class="line">            <span class="keyword">if</span> (matrix[i][j] !== <span class="literal">null</span>)&#123;</span><br><span class="line">                count += <span class="number">1</span>;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> count === <span class="number">9</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">app.use(<span class="string">'/static'</span>, express.static(<span class="string">'static'</span>));</span><br><span class="line">app.use(bodyParser.json());</span><br><span class="line">app.set(<span class="string">'view engine'</span>, <span class="string">'html'</span>);</span><br><span class="line">morganBody(app);</span><br><span class="line">app.engine(<span class="string">'html'</span>, <span class="built_in">require</span>(<span class="string">'hbs'</span>).__express);</span><br><span class="line"></span><br><span class="line">app.get(<span class="string">'/'</span>, (req, res) =&gt; &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">0</span>; i &lt; <span class="number">3</span>; i++)&#123;</span><br><span class="line">        matrix[i] = [<span class="literal">null</span> , <span class="literal">null</span>, <span class="literal">null</span>];</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">    res.render(<span class="string">'index'</span>);</span><br><span class="line">&#125;)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">app.get(<span class="string">'/admin'</span>, (req, res) =&gt; &#123; </span><br><span class="line">    <span class="comment">/*this is under development I guess ??*/</span></span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span>(user.admintoken &amp;&amp; req.query.querytoken &amp;&amp; md5(user.admintoken) === req.query.querytoken)&#123;</span><br><span class="line">        res.send(<span class="string">'Hey admin your flag is &lt;b&gt;flag&#123;prototype_pollution_is_very_dangerous&#125;&lt;/b&gt;'</span>);</span><br><span class="line">    &#125; </span><br><span class="line">    <span class="keyword">else</span> &#123;</span><br><span class="line">        res.status(<span class="number">403</span>).send(<span class="string">'Forbidden'</span>);</span><br><span class="line">    &#125;   </span><br><span class="line">&#125;</span><br><span class="line">)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">app.post(<span class="string">'/api'</span>, (req, res) =&gt; &#123;</span><br><span class="line">    <span class="keyword">var</span> client = req.body;</span><br><span class="line">    <span class="keyword">var</span> winner = <span class="literal">null</span>;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (client.row &gt; <span class="number">3</span> || client.col &gt; <span class="number">3</span>)&#123;</span><br><span class="line">        client.row %= <span class="number">3</span>;</span><br><span class="line">        client.col %= <span class="number">3</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    matrix[client.row][client.col] = client.data;</span><br><span class="line">    <span class="built_in">console</span>.log(matrix);</span><br><span class="line">    <span class="keyword">for</span>(<span class="keyword">var</span> i = <span class="number">0</span>; i &lt; <span class="number">3</span>; i++)&#123;</span><br><span class="line">        <span class="keyword">if</span> (matrix[i][<span class="number">0</span>] === matrix[i][<span class="number">1</span>] &amp;&amp; matrix[i][<span class="number">1</span>] === matrix[i][<span class="number">2</span>] )&#123;</span><br><span class="line">            <span class="keyword">if</span> (matrix[i][<span class="number">0</span>] === <span class="string">'X'</span>) &#123;</span><br><span class="line">                winner = <span class="number">1</span>;</span><br><span class="line">            &#125;</span><br><span class="line">            <span class="keyword">else</span> <span class="keyword">if</span>(matrix[i][<span class="number">0</span>] === <span class="string">'O'</span>) &#123;</span><br><span class="line">                winner = <span class="number">2</span>;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">if</span> (matrix[<span class="number">0</span>][i] === matrix[<span class="number">1</span>][i] &amp;&amp; matrix[<span class="number">1</span>][i] === matrix[<span class="number">2</span>][i])&#123;</span><br><span class="line">            <span class="keyword">if</span> (matrix[<span class="number">0</span>][i] === <span class="string">'X'</span>) &#123;</span><br><span class="line">                winner = <span class="number">1</span>;</span><br><span class="line">            &#125;</span><br><span class="line">            <span class="keyword">else</span> <span class="keyword">if</span>(matrix[<span class="number">0</span>][i] === <span class="string">'O'</span>) &#123;</span><br><span class="line">                winner = <span class="number">2</span>;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (matrix[<span class="number">0</span>][<span class="number">0</span>] === matrix[<span class="number">1</span>][<span class="number">1</span>] &amp;&amp; matrix[<span class="number">1</span>][<span class="number">1</span>] === matrix[<span class="number">2</span>][<span class="number">2</span>] &amp;&amp; matrix[<span class="number">0</span>][<span class="number">0</span>] === <span class="string">'X'</span>)&#123;</span><br><span class="line">        winner = <span class="number">1</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (matrix[<span class="number">0</span>][<span class="number">0</span>] === matrix[<span class="number">1</span>][<span class="number">1</span>] &amp;&amp; matrix[<span class="number">1</span>][<span class="number">1</span>] === matrix[<span class="number">2</span>][<span class="number">2</span>] &amp;&amp; matrix[<span class="number">0</span>][<span class="number">0</span>] === <span class="string">'O'</span>)&#123;</span><br><span class="line">        winner = <span class="number">2</span>;</span><br><span class="line">    &#125; </span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (matrix[<span class="number">0</span>][<span class="number">2</span>] === matrix[<span class="number">1</span>][<span class="number">1</span>] &amp;&amp; matrix[<span class="number">1</span>][<span class="number">1</span>] === matrix[<span class="number">2</span>][<span class="number">0</span>] &amp;&amp; matrix[<span class="number">2</span>][<span class="number">0</span>] === <span class="string">'X'</span>)&#123;</span><br><span class="line">        winner = <span class="number">1</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (matrix[<span class="number">0</span>][<span class="number">2</span>] === matrix[<span class="number">1</span>][<span class="number">1</span>] &amp;&amp; matrix[<span class="number">1</span>][<span class="number">1</span>] === matrix[<span class="number">2</span>][<span class="number">0</span>] &amp;&amp; matrix[<span class="number">2</span>][<span class="number">0</span>] === <span class="string">'O'</span>)&#123;</span><br><span class="line">        winner = <span class="number">2</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (draw(matrix) &amp;&amp; winner === <span class="literal">null</span>)&#123;</span><br><span class="line">        res.send(<span class="built_in">JSON</span>.stringify(&#123;<span class="attr">winner</span>: <span class="number">0</span>&#125;))</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">else</span> <span class="keyword">if</span> (winner !== <span class="literal">null</span>) &#123;</span><br><span class="line">        res.send(<span class="built_in">JSON</span>.stringify(&#123;<span class="attr">winner</span>: winner&#125;))</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">else</span> &#123;</span><br><span class="line">        res.send(<span class="built_in">JSON</span>.stringify(&#123;<span class="attr">winner</span>: <span class="number">-1</span>&#125;))</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;)</span><br><span class="line">app.listen(<span class="number">3000</span>, () =&gt; &#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">'app listening on port 3000!'</span>)</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>
<p>查看源码可知，我们需要令<code>md5(user.admintoken) === req.query.querytoken</code> 且 <code>user.admintoken存在</code>,而源码中显示user是个 <code>[]类</code>这个类并没有开发完成,所以我们的目标就是给user.admintoken赋值.</p>
<p>根据原型链的概念,当user.admintoken没有值时,会递归访问<strong>proto</strong>查询,所以我们可以尝试寻找某个<code>[]类</code>并修改它的原型.<br>在<code>/api</code>接口中,函数会接收传参,并<code>matrix[client.row][client.col] = client.data;</code>.<br>而matrix[“<strong>proto</strong>“]就是matrix对象的原型,这样就造成了原型链污染.</p>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/6.png" alt="test"></p>
<p>payload:<br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/7.png" alt="test"><br><img src="//desperadoccy.github.io/2020/10/01/js原型污染/8.png" alt="test"></p>
<h3 id="xss13"><a href="#xss13" class="headerlink" title="xss13"></a>xss13</h3><p><a href="http://prompt.ml/13" target="_blank" rel="noopener">靶场地址</a></p>
<p>源码如下</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"> <span class="function"><span class="keyword">function</span> <span class="title">escape</span>(<span class="params">input</span>) </span>&#123;</span><br><span class="line">    <span class="comment">// extend method from Underscore library</span></span><br><span class="line">    <span class="comment">// _.extend(destination, *sources) </span></span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">extend</span>(<span class="params">obj</span>) </span>&#123;</span><br><span class="line">        <span class="keyword">var</span> source, prop;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">var</span> i = <span class="number">1</span>, length = <span class="built_in">arguments</span>.length; i &lt; length; i++) &#123;</span><br><span class="line">            source = <span class="built_in">arguments</span>[i];</span><br><span class="line">            <span class="keyword">for</span> (prop <span class="keyword">in</span> source) &#123;</span><br><span class="line">                obj[prop] = source[prop];</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> obj;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">// a simple picture plugin</span></span><br><span class="line">    <span class="keyword">try</span> &#123;</span><br><span class="line">        <span class="comment">// pass in something like &#123;"source":"http://sandbox.prompt.ml/PROMPT.JPG"&#125;</span></span><br><span class="line">        <span class="keyword">var</span> data = <span class="built_in">JSON</span>.parse(input);</span><br><span class="line">        <span class="keyword">var</span> config = extend(&#123;</span><br><span class="line">            <span class="comment">// default image source</span></span><br><span class="line">            source: <span class="string">'http://placehold.it/350x150'</span></span><br><span class="line">        &#125;, <span class="built_in">JSON</span>.parse(input));</span><br><span class="line">        <span class="comment">// forbit invalid image source</span></span><br><span class="line">        <span class="keyword">if</span> (<span class="regexp">/[^\w:\/.]/</span>.test(config.source)) &#123;</span><br><span class="line">            <span class="keyword">delete</span> config.source;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">// purify the source by stripping off "</span></span><br><span class="line">        <span class="keyword">var</span> source = config.source.replace(<span class="regexp">/"/g</span>, <span class="string">''</span>);</span><br><span class="line">        <span class="comment">// insert the content using mustache-ish template</span></span><br><span class="line">        <span class="keyword">return</span> <span class="string">'&lt;img src="&#123;&#123;source&#125;&#125;"&gt;'</span>.replace(<span class="string">'&#123;&#123;source&#125;&#125;'</span>, source);</span><br><span class="line">    &#125; <span class="keyword">catch</span> (e) &#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">'Invalid image data.'</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>我们分析下源码</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">try</span> &#123;</span><br><span class="line">        <span class="comment">// pass in something like &#123;"source":"http://sandbox.prompt.ml/PROMPT.JPG"&#125;</span></span><br><span class="line">        <span class="keyword">var</span> data = <span class="built_in">JSON</span>.parse(input);</span><br><span class="line">        <span class="keyword">var</span> config = extend(&#123;</span><br><span class="line">            <span class="comment">// default image source</span></span><br><span class="line">            source: <span class="string">'http://placehold.it/350x150'</span></span><br><span class="line">        &#125;, <span class="built_in">JSON</span>.parse(input));</span><br><span class="line">        <span class="comment">// forbit invalid image source</span></span><br><span class="line">        <span class="keyword">if</span> (<span class="regexp">/[^\w:\/.]/</span>.test(config.source)) &#123;</span><br><span class="line">            <span class="keyword">delete</span> config.source;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">// purify the source by stripping off "</span></span><br><span class="line">        <span class="keyword">var</span> source = config.source.replace(<span class="regexp">/"/g</span>, <span class="string">''</span>);</span><br><span class="line">        <span class="comment">// insert the content using mustache-ish template</span></span><br><span class="line">        <span class="keyword">return</span> <span class="string">'&lt;img src="&#123;&#123;source&#125;&#125;"&gt;'</span>.replace(<span class="string">'&#123;&#123;source&#125;&#125;'</span>, source);</span><br><span class="line">    &#125; <span class="keyword">catch</span> (e) &#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">'Invalid image data.'</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>主函数将用户传参进行<code>JSON.parse(input)</code>替换成原有的图片资源,这边造成了原型链污染.<br>如果我们传入的source值不符合正则,他将删除<code>config.source</code></p>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/9.png" alt="test"></p>
<p>我们尝试传入<code>{&quot;source&quot;:&quot;*&quot;, &quot;__proto__&quot;: {&quot;source&quot;:&quot;1&quot;}}</code>,验证了我们之前的分析</p>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/10.png" alt="test"></p>
<p>接下来要做的就是xss注入的绕过<code>&quot;</code>了<br>查看js文档中replace函数性质:</p>
<blockquote>
<p>   字符串 stringObject 的 replace() 方法执行的是查找并替换的操作。它将在 stringObject 中查找与 regexp 相匹配的子字符串，然后用 replacement 来替换这些子串。如果 regexp 具有全局标志 g，那么 replace() 方法将替换所有匹配的子串。否则，它只替换第一个匹配子串。<br>    replacement 可以是字符串，也可以是函数。如果它是字符串，那么每个匹配都将由字符串替换。但是 replacement 中的 $ 字符具有特定的含义。如下表所示，它说明从模式匹配得到的字符串将用于替换。<br>    <img src="//desperadoccy.github.io/2020/10/01/js原型污染/11.png" alt="test"></p>
</blockquote>
<p>我们先来测试下这个特性</p>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/12.png" alt="test"></p>
<p>这样我们就可以通过<code>&#39;&lt;img src=&quot;_posts/js原型污染.md&quot;&gt;&#39;.replace(&#39;_posts/js原型污染.md&#39;, source)</code>中_posts/js原型污染.md前的<code>&quot;</code>来闭合,进而注入</p>
<p>payload如下:</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">&#123;<span class="string">"source"</span>:<span class="string">"*"</span>, <span class="string">"__proto__"</span>: &#123;<span class="string">"source"</span>:<span class="string">"$`  onerror='prompt(1)' "</span>&#125;&#125;</span><br></pre></td></tr></table></figure>
<p><img src="//desperadoccy.github.io/2020/10/01/js原型污染/13.png" alt="test"></p>
<h3 id="Thejs"><a href="#Thejs" class="headerlink" title="Thejs"></a>Thejs</h3><p>题目源码地址<a href="https://github.com/phith0n/code-breaking/blob/master/2018/thejs" target="_blank" rel="noopener">https://github.com/phith0n/code-breaking/blob/master/2018/thejs</a><br>题目部署地址<a href="http://106.15.177.94:10025/" target="_blank" rel="noopener">http://106.15.177.94:10025/</a></p>
<p>看了很多wp,不太清楚清楚师傅们是怎么泄露到源码或者fuzz到注入点的,可能是赛程中放出了主要代码吧.<br>这里就直接分享p神的题解了<a href="https://www.leavesongs.com/PENETRATION/javascript-prototype-pollution-attack.html" target="_blank" rel="noopener">深入理解 JavaScript Prototype 污染攻击</a></p>
<h2 id="参考资料"><a href="#参考资料" class="headerlink" title="参考资料"></a>参考资料</h2><p><a href="https://juejin.im/post/6844903567375990791" target="_blank" rel="noopener">三分钟看完JavaScript原型与原型链</a><br><a href="https://www.smi1e.top/javascript-%E5%8E%9F%E5%9E%8B%E9%93%BE%E6%B1%A1%E6%9F%93/" target="_blank" rel="noopener">JavaScript 原型链污染</a><br><a href="https://www.leavesongs.com/PENETRATION/javascript-prototype-pollution-attack.html" target="_blank" rel="noopener">深入理解 JavaScript Prototype 污染攻击</a><br><a href="https://xz.aliyun.com/t/7182" target="_blank" rel="noopener">浅析javascript原型链污染攻击</a></p>

      
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                    isMatch = true;
                    hitCount = indexOfTitle.length + indexOfContent.length;
                  }
                }

                // show search results

                if (isMatch) {
                  // sort index by position of keyword

                  [indexOfTitle, indexOfContent].forEach(function (index) {
                    index.sort(function (itemLeft, itemRight) {
                      if (itemRight.position !== itemLeft.position) {
                        return itemRight.position - itemLeft.position;
                      } else {
                        return itemLeft.word.length - itemRight.word.length;
                      }
                    });
                  });

                  // merge hits into slices

                  function mergeIntoSlice(text, start, end, index) {
                    var item = index[index.length - 1];
                    var position = item.position;
                    var word = item.word;
                    var hits = [];
                    var searchTextCountInSlice = 0;
                    while (position + word.length <= end && index.length != 0) {
                      if (word === searchText) {
                        searchTextCountInSlice++;
                      }
                      hits.push({position: position, length: word.length});
                      var wordEnd = position + word.length;

                      // move to next position of hit

                      index.pop();
                      while (index.length != 0) {
                        item = index[index.length - 1];
                        position = item.position;
                        word = item.word;
                        if (wordEnd > position) {
                          index.pop();
                        } else {
                          break;
                        }
                      }
                    }
                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
                    slicesOfTitle.push(mergeIntoSlice(title, 0, title.length, indexOfTitle));
                  }

                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  
  

  

  

  

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